Silicon wafers are used in the fabrication of integrated circuits (ICs) and other microelectronic systems (MEMS) devices. The wafer serves as the substrate for fabrication of microelectronic devices built in and over the wafer. The wafer therefore undergoes many microfabrication process steps. Once the desired functionality is achieved, the individual devices are separated and packaged.
Silicon wafers, however, have limited functionality. For example, silicon wafers can be fabricated for the purposes of digital or analog processing but are unable to efficiently serve as light emitters and detectors. Rather light emitters and light detectors are typically fabricated from wafers made of compound semiconductor materials, such as group III-V semiconductor materials. In particular, compound semiconductor devices have stronger optical absorption, electrically driven optical emission, high and low band-gaps and higher carrier mobilities than silicon devices. Silicon devices, however, have the advantage of high performance IC processing, materials and micromachining technology.
In many microelectronic systems (MEMS) and optoelectronic applications, it is desirable to use compound semiconductor devices and silicon devices in combination. Combining the devices into one structure, however, has been challenging from a technical standpoint making it commercially unfeasible.